The search for oxide materials with physical properties similar to the cuprate high Tc superconductors, but based on alternative transition metals such as nickel, has grown and evolved over time [1][2][3][4][5][6][7][8][9][10]. The recent discovery of superconductivity in doped infinite-layer nickelates RNiO2 (R = rare-earth element) [11,12] further strengthens these efforts. With a crystal structure similar to the infinite-layer cupratestransition metal oxide layers separated by a rare-earth spacer layerformal valence counting suggests that these materials have monovalent Ni 1+ cations with the same 3d electron count as Cu 2+ in the cuprates. Here, we use x-ray spectroscopy in concert with density functional theory to show that the electronic structure of RNiO2 (R = La, Nd), while similar to the cuprates, includes significant distinctions. Unlike cuprates with insulating spacer layers between the CuO2 planes, the rare-earth spacer layer in the infinite-layer nickelate supports a weaklyinteracting three-dimensional 5d metallic state. This three-dimensional metallic state hybridizes with a quasi-two-dimensional, strongly correlated state with 3dx 2 -y 2 symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare earth intermetallics [13-15], well-known for heavy Fermion behavior, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy Fermion compounds. This unique Kondo-or Anderson-lattice-like "oxide-intermetallic" replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.While the mechanism of superconductivity in the cuprates remains a subject of intense research, early on it was suggested that the conditions required for realizing high Tc superconductivity are rooted in the physics of a two-dimensional electron system subject to strong local repulsion [16,17]. This describes the Mott (charge-transfer) insulators in the stoichiometric parent compounds, characterized by spin ½ Heisenberg antiferromagnetism, from which superconductivity emerges upon doping. A long-standing question regards whether these "cuprate-Mott" conditions can be realized in other oxides; and extensive efforts to synthesize and engineer nickel oxides (nickelates) have promised such a realization [1-10]. Infinite-layer NdNiO2 became the first such nickelate superconductor following the recent discovery of superconductivity in Srdoped samples [11]. The undoped parent compound, produced by removing the apical oxygen atoms from the perovskite nickelate NdNiO3 using a metal hydride-based soft chemistry reduction process [10,[18][19][20], appears to be a close sibling of the cuprates-it is isostructural to the infinitelayer cuprates with monovalent Ni 1+ cations and possesses the same 3d 9 electron count as that of Cu 2+ cations in undoped cuprates. Yet, as we will reveal, the electronic structure of the undoped RNiO2 (R = La and Nd) remains distinct from the Mott, or charge-transfer, compounds of undoped cuprates, and even...
In this paper, a new kind of 2D piezotronic transistor (PT) with the highest sensitivity till date has been designed and demonstrated, and the 2DPT array with ultrahigh spatial resolution has been developed through assembling ZnO nanoplatelets into ordered nanoplatelet array. As active sensors by directly converting applied mechanical actuations into electrical control signals without applying gate voltage, the ZnO 2DPT array has a great advantage as a fundamental component of piezotronics. The 2DPT array paves the way for a large-scale and integrated production of two terminal vertical transistors, which will contribute to its application in many fields such as human-machine interfacing, smart sensor, and processor systems.
Measurement of nonlinear response offers powerful probes of material propertiesnot accessible at linear order, as they follow distinct symmetry requirements 1,2,3,4,5,6 . For instance, unlike the linear Hall effect, the second-order nonlinear Hall effect typically requires the breaking of inversion symmetry rather than time reversal symmetry 1 , and its successful detection in recent experiments on ultrathin WTe2 has attracted significant attention 7,8 . This second-order nonlinear Hall effect could be used to probe the Berry curvature, a band geometric property, in non-magnetic materials, just like the anomalous Hall effect being used to probe the Berry curvature in magnetic materials 9,10 . As another intrinsic band geometric property, the Berry-connection polarizability tensor was theoretically predicted to play a crucial role in high-order responses 11 but not yet experimentally demonstrated. Here, we report for the first time a high-order nonlinear Hall effect in multi-layer 𝑻 𝒅 -MoTe2 samples. Unprecedently, the third-order Hall
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